The reactivity and adaptability of the microvilli and lysosomes of the small intestine towards different dietary and hormonal stimuli will be studied during the postnatal development of the rat. BIBLIOGRAPHIC REFERENCES: Celano, P., Jumawan, J., Horowitz, C., Lau, H. and Koldovsky, O. Prenatal induction of sucrase activity in rat jejunum. Biochem. J. (1977) in press. Kendall, K., Koldovsky, O., Jumawan, J., Celano, P. and Krulich, L. Effect of the host hormonal status on development of sucrase and acid beta-galactorsidase in isografts of rat small intestine. Fed. Proc. 36:1977.